The main function of the vascular endothelium is the mediation and control of the transendothelial exchanges of water and solutes (both small and large molecules) between blood plasma and the interstitial fluid, in short the control of vascular permeability. This function is obviously "vital", being critical for normal growth, maintenance and survival of all the cells from all tissues and organs. It is also an important contributor to the defense mechanisms that occur in inflammation. While the morphological structures involved in transendothelial exchanges have been identified (i.e. caveolae, endothelial specific organelles such as transendothelial channels, fenestrae, vesiculo-vacuolar organelles as well as intercellular junctions), with the exception of caveolae and the intercellular junctions, there is very little to no biochemical evidence on the molecular composition of the structures involved, their biogenesis and regulation. The major goals of this research proposal are to elucidate the mechanism of endothelial fenestrae biogenesis. Besides their impact on the understanding of the normal physiological process of the transendothelial exchange, the data could be used further in the study of the pathophysiology of several human diseases such as tumor angiogenesis, acute and chronic inflammation (both viral and bacterial infections, transplant rejection, allergic encephalomyelytis, Alzheimer disease), atherosclerosis, preeclampsia, toxic liver injury and cirrhosis where modulations of endothelial fenestrae have been shown to occur. These studies could also help in designing novel strategies for drugs and gene targeting to selected microvascular beds. The techniques employed are cell isolation, fractionation, biochemical assays, cell free-assays, genetically modified animal models, cell culture, transfections, light and electron microscopy.